The present invention relates to a method for recording images or pictures with utilizing electrostatic latent image, and particularly to a picture recording method for obtaining toner image by developing, without disturbance, visualized image (toner image) formed previously on latent image carrier.
Various color image recording methods utilizing electronic photography method have been proposed. As such color picture recording method, for example, so-called a repeated developing method has been proposed. The repeated developing method obtains color picture by the processes that the electrostatic latent images of two or three levels are formed on a single photosensitive medium, the first latent image of photosensitive medium having such latent images of two or three levels is developed by a first developing device, thereafter the second latent image on the photosensitive medium is developed by a second developing device and a finally formed toner image is then transferred at a time. This method is very effective in realizing reduction of size and high copying speed.
However, in such repeated developing method, the photosensitive medium carrying toner image through the first developing process is then rubbed by the developer in the second and successive processes and thereby the toner image formed by the first developing process is disturbed remarkably by the second and successive developing processes. As a result, this method is accompanied by the problem that the color picture finally obtained is considerably disturbed. Therefore, it is a very important subject for the picture forming method utilizing the repeated developing method to realize the development of the successive stages without disturbing toner images of preceding stages.
It is also considered to achieve the developing processes in the successive stages with the single-element non-contact development in order not to disturb the toner image on the photosensitive medium. However, the single-element non-contact development has difficulty of high speed operation and it is therefore desirable, from this point of view, to use the double-element developer consisting of carrier and toner.
However, in the magnetic brush developing method, development is carried out by depositing the double-element developer on a non-magnetic sleeve having a magnet roll therein and rubbing a latent image with magnetic brush. However, in the repeated developing method, the toner image formed in the developing process of the preceding stage is disturbed because the toner image is rubbed with the tip part of the magnetic brush in the developing process of the succeeding stage.
As a means for solving such problems, the Japanese patent application unexamined publication No. 126665/1985 proposes a color image developing device which uses the double-element developer mixing the magnetic carrier with its grain size of 50 .mu.m or less with the toner particle. However, reduction in grain size of carrier improves disturbance of image, but when the grain size becomes smaller, the more carrier transfers to the surface of photosensitive medium from the developing device, namely the carry over phenomenon becomes more distinctive. In order to avoid the, carry over phenomenon, a magnetic force must be enhanced as much. Accordingly, it is required to make large a certain degree the grain size of carrier particle. Therefore, only regulation of grain size of carrier cannot result in sufficiently satisfied result.
On the other hand, various image forming methods to easily form and record composite pictures utilizing electronic photography method have been proposed. As such a picture forming method, a so-called repeated negative exposing method is typical as the method using a single developing device. In this method, after the photosensitive medium of the electronic photography is uniformly charged, a latent image of first picture is negatively written on the photosensitive medium by the exposing means to expose image parts. A latent image of second picture is also formed by the negative writing method to combine the second picture with the first picture and the first and second latent images are inversed at a time to form the composite picture.
Meanwhile, as a composite picture forming method utilizing two developing devices, a method to form a combined picture by the process consisting of charging, first negative (or positive) image exposing, second positive (or negative) image exposing, first developing (regular developing or inverse developing) and second developing (inverse developing or regular developing) is already known.
Moreover, the Japanese patent application unexamined publication No. 2047/1982 discloses a method utilizing the image forming process consisting of charging--first negative image exposing--first developing (inverse developing)--second positive image exposing--second developing (regular developing).
However, the repeated negative image exposing method is certainly simplified in the structure but also has a disadvantage that the pictures cannot be combined on the ordinary positive document.